PET imaging for thyroid cancers: Current status and future directions

Positron emission tomography-computed tomography (PET/CT) combines both functional and anatomic information and provides in vivo molecular information on biological processes that can be useful at different steps of evolution of thyroid cancers. ¹⁸Fluorodeoxyglucose being highly trapped in rapidly dividing cells makes ¹⁸F-FDG-PET recommended in the staging, prognostic evaluation and follow-up of metastatic and/or of poorly differentiated thyroid carcinomas. ¹⁸F-FDG PET/CT can help in the localization of persistent/recurrent disease. However, its sensitivity depends widely on tumor burden and histology. Iodine 124 (¹²⁴I) is currently under evaluation for diagnosis and pretherapeutic dosimetry planning. PET/CT using ¹⁸F-FDOPA is the most sensitive radiopharmaceutical for localizing persistent/recurrent medullary thyroid carcinoma (MTC). However, its sensitivity depends on calcitonin levels, with a threshold value of around 150pg/mL. ¹⁸F-FDG PET/CT can also be used in MTC with short calcitonin or CEA doubling time.